1. Field of the Invention
The present invention relates to devices for preventing idle driving operations of fastener driving tools, and in particular to devices operable to inhibit fasteners, such as nails, from being driven out of a tool body of a driving tool, such as a nailing machine and a pin tacker when all or some the fasteners stored within a magazine have been discharged. The magazine stores the fasteners and serves to feed the fasteners into the tool body one after another. The present invention also relates to fastener driving tools having the devices for preventing the idle driving operations.
2. Description of the Related Art
Known tools for driving thin nails, which arm used for finishing works, have a magazine for storing the nails in a flat plate-like form. Thus, the thin nails are arranged parallel with each other and joined together, while the nails can be separated from each other. The nails in the flat plate-like form are fed from the magazine one after another into a driving channel defined in a tool body as a driving device is operated.
Various improvements have been made to this kind of tools. For example, U.S. Pat. No. 5,180,091 teaches an idle driving operation preventing device that can inhibit the operation of a driving device when all the nags within a magazine have been discharged.
The idle driving operation preventing device of the above patent is schematically shown in FIGS. 13 and 14 and is labeled with reference numeral 50. The conventional device 50 has a switch lever 51 and a stopper member 52 connected to the switch lever 51. The stopper member 52 extends into a magazine 53 in order to intervene in a moving path of a pusher 54. When no remaining nail exists within a fastener storing region 53a of the magazine 53 or when no nail has been has been fed into a fastener driving channel 58 of a tool body, an engaging portion 54a of the pusher 54 engages an engaging portion 52a of the stopper member 52, so that the upward movement of the switch lever 51 for turning on the switch lever 51 is inhibited. Therefore, the idle driving operation of the fasteners by a driver 57 can be prevented. FIG. 14 shows the state where the idle driving operation has been prevented.
However, the conventional idle driving operation preventing device has the following problems. Thus, as shown in FIGS. 13 and 14, the moving direction of the stopper member 52 (vertical direction in FIGS. 13 and 14) is set to be perpendicular to a feeding direction of the nails by the pusher 54 (left direction in FIGS. 13 and 14). In addition, in order to reliably feed the nails in the feeding direction, the nails are biased in the feeding direction by a compression spring 55 that has a relatively strong spring force. On the other hand, the switch lever 51 with the stopper member 52 is biased downward toward an off position by a compression spring 56 that has a spring force smaller than that of the compression spring 55.
Therefore, when the last nail within the magazine 53 has been driven and the pusher 54 has moved further to the left side, the engaging portion 54a of the pusher 54 may be pressed against the side surface of the stopper member 52 by the strong force of the compression spring 55 as shown in FIG. 13 prior to achieving the idle driving preventing condition shown in FIG. 14. Because the strong spring force of the compression spring 55 may produce a strong resistance force against the movement of the stopper member 52, a possibility may exist that the switch lever 51 with the stopper member 52 may not move downward toward the off position by the small spring force of the compression spring 56. When this occurs, the idle driving preventing device will not operate.